Metal part with controlled deformation orientation

ABSTRACT

A metal piece having at least two areas of lower mechanical strength than the body of the piece, said pieces being respectively arranged on one side and the other of a longitudinal central section (PM) of said piece and alternatively located in two locations separated longitudinally along the piece, the areas of lower mechanical strength than the body of the piece being formed by local control of the stamping temperature during a stamping process of the piece, notably a process comprising steps including heating the piece to a temperature range suitable for obtaining an austenitic stage, then stamping this piece in a stamping tool suitable for defining different temperatures in the different areas of the stamped piece, for example by virtue of the voids formed in the stamping tool or by local reheating of the stamping tool.

FIELD OF THE INVENTION

This invention relates to the field of metal pieces that form a piece ofthe manufacture of a metal framework, notably of a chassis or bodyworkor body of vehicles.

STATE OF THE ART

Examples of manufacturing known pieces can be found in the documentsWO2006/038868, WO2009/123538, EP2143621, EP2565489, US2009/072586,JP2011/173166, JP07/119892, US2007/052258, GB2344794, WO00/03909,DE10257262 and DE102006048429.

GENERAL OBJECTIVE OF THE INVENTION

The aim of the present invention is to propose means that enable theaccurate control of the nature and orientation of the deformation of ametal piece, preferably elongated and/or compact.

The above-mentioned goal is achieved according to the invention due to ametal piece having at least two mechanical resistance areas below thebody of the piece, arranged respectively on one side and the other of alongitudinal center section on the said piece, alternatively in placeslongitudinally separated along the length of the piece.

According to another aspect of the invention, the metal piece comprisesa bottom to the piece and two side flanges separated from the bottom ofthe piece by walls, the section of the metal piece being duly defined bytwo reference axes, one being substantially orthogonal to the bottom ofthe piece and the other entirely parallel to at least one flange, andthe piece comprises an area of lower mechanical strength established atthe time of stamping and that runs along at least one of the walls,asymmetrically with respect to the reference axes.

According to another aspect of the invention, the metal piece comprisesa bottom to the piece and two side flanges separated from the bottom ofthe piece by walls, and the piece comprises an area of lower mechanicalstrength established at the time of stamping that has a varying widthperpendicularly to a cross-section plane of the piece.

Regarding other characteristics, the purposes and advantages of thepresent invention will emerge upon reading the following detaileddescription and upon viewing the attached designs and drawings given asnon-limitative examples and regarding which:

FIGS. 1a, 1b, 1c, and 1d are drawings of the cross-sections of fourgeneral variants of the manufacture of the pieces to which the inventionmay be applied,

FIGS. 2a to 2k represent different examples of manufacture of metalpieces in accordance with the present invention comprising at least twoareas of lower mechanical strength than the body of the piece, arrangedrespectively on one side and the other of a central longitudinal sectionof said piece,

FIGS. 3a to 3f represent six non-limitative examples of pieces inaccordance with variants of the present invention comprising reducedmechanical strength and a varying length,

FIG. 4 represents a comparative diagram of the bending moments obtainedaccording to 4 bending axes, respectively for a piece in accordance withthe invention represented in FIG. 6A having an area of lower mechanicalstrength limited to a portion of its cross-section and for a classicexample represented by FIG. 7A, having an area of lower mechanicalstrength on the entirety of its cross-section,

FIG. 5 represents the bending moments curve over time, around axis Z,respectively for the piece in accordance with the invention representedin FIG. 6A, and for the classic example represented by FIG. 7A, and foran alternative variant of the piece in accordance with the inventionrepresented in FIG. 6Abis,

FIGS. 6B, 6Bbis and 7B represent cross-section views of the same piecesand display the placement of the areas of lower mechanical strength,whereas FIGS. 6C, 6Cbis and 7C represent the bending of pieces aroundaxis Z corresponding to the curves illustrated in FIG. 5,

FIGS. 8a, 8b, 8c and 8d represent four non-limitative variants of thesection of pieces in accordance with the present invention and displayspreferred flexural axes for these pieces, whereas FIGS. 8a bis, 8 bbis,8 cbis and 8 dbis show a central longitudinal section for these pieces,

FIG. 9 represents the bending moments curve over time, around axis Y,respectively for the piece in accordance with the invention representedin FIG. 6A, and for the classic example represented by FIG. 7A, and foran alternative variant of the piece in accordance with the inventionrepresented in FIG. 6Abis,

the FIGS. 6D and 7D represent the flexures of the piece in accordancewith the invention represented in FIG. 6A and for the classic examplerepresented by FIG. 7A around axis Y corresponding to the curvesillustrated in FIG. 9,

la FIG. 10 represents the bending moments curve over time, respectivelyfor the piece in accordance with the invention represented in FIG. 6A,for the classic example represented by FIG. 7A and for the alternativevariant of the piece in accordance with the invention represented inFIG. 6Abis, around axis Z and this respectively in the desired bendingdirection and in the opposite direction,

FIGS. 6C1, identical to FIG. 6C, and 6E represent the bending moments ofthe piece in accordance with the invention represented in FIG. 6A aroundaxis Z and this respectively in the desired bending direction and in theopposite direction.

We shall now describe 4 examples of those pieces in which the presentinvention can be applied, with regard to FIGS. 1a to 1d . These figuresrepresent the straight section, or “cross-section”, of four alternativeembodiments, along a plane perpendicular to a main longitudinal axis forthe pieces. This main longitudinal axis for the pieces will be similarlynamed “main axis of extension” hereinafter. In this way, the illustratedpieces preferably have a constant straight section along their entirelength that corresponds to the representation given in FIGS. 1a to 1d .According to an alternative however, the cross-section of the pieces maybe developed lengthwise along the pieces.

We have shown in the FIGS. 1a, 1b and 1c , attached herein, differentexemplary embodiments of the metal pieces comprising a bottom 10 to thepiece and two side flanges 30, 32, separated from the bottom 10 of thepiece by walls 20, 22.

According to the embodiment in FIG. 1a , the piece, generallyhat-shaped, comprises a U-shaped body 12 comprising a core that formsthe bottom 10 of the piece and two flanges entirely orthogonal to thebottom 10 and forming the walls 20, 22. The side grooves 30, 32,extending entirely orthogonally to the walls 20, 22 and thereforeentirely parallel to the bottom 10 of the piece according to FIG. 1 a.

According to FIG. 1b , the body is generally L-shaped comprising a corethat forms the bottom 10 of the piece, a flange substantially orthogonalto the bottom 10 and forming a wall 20, a first flange 30 that extendssubstantially orthogonally to the wall 20 and therefore substantiallyparallel to the bottom 10 of the piece, a second flange 22 that extendsparallel to the bottom 10 of the piece and forms a second wall 22, and aflange 32 which stretches out entirely in the projection of the core 22.

According to FIG. 1c , the body is formed by a substantially flat sheetin such a way that the two walls 20, 22 are substantially located withinthe projection of the core forming the bottom 10 of the piece and thetwo flanges 30, 32 are similarly substantially within the projection ofthe walls 20, 22.

According to the three embodiments represented in the FIGS. 1a, 1b and1c , the two flanges 30, 32 are parallel to each other. However, thisarangement is by no means limiting. Variants in which the two flanges30, 32 are at least slightly inclined with respect to the other can beenvisaged.

As can be seen in the FIGS. 1a, 1b and 1c , in each one of thealternative embodiments, the metal piece has a cross-section defined bytwo reference axes, one A-A substantially orthogonal to the bottom 10 ofthe piece and the other B-B substantially parallel to at least oneflange.

Moreover, an alternative embodiment is represented in FIG. 1d .According to this embodiment, the piece is a tubular piece comprising,but not limited to, a section defined by four substantially flat walls40, 42, 44 and 46, respectively parallel and orthogonal in pairs.

Again, the piece outlined in FIG. 1d comprises two reference axes, oneA-A substantially orthogonal to the walls 40, 42 and parallel to thewalls 44, 46 and the other B-B wholly parallel to the walls 40, 42 andorthogonal to the walls 44 and 46.

FIGS. 2a through 2k represent different exemplary embodiments of metalpieces in accordance with the present invention comprising at least twoareas of lower mechanical strength than the body of the piece, arrangedrespectively on both side of central longitudinal section PM of theaforementioned piece passing through the reference axis A-A.

The invention applies to elongated pieces having a main elongation axisor “main extension axis”.

The cross-sections of the pieces are cross-sections in planesperpendicular to this elongation axis or main axis along which the pieceextends.

In the context of this present application, it is understood that“central longitudinal cross-section” refers to a longitudinalcross-section that passes through centers of inertia or gravity of twocross-sections in the piece located close to the ends of a portion, thelongitudinal cross-section extending in accordance with the mainelongation axis.

More precisely, the “central longitudinal cross-section” is alongitudinal section of a piece that passes through the main axis alongwhich the piece extends, this axis itself passing through centers ofinertia of the cross-section of the piece (single piece made frommaterials or to be assembled from several elementary pieces)perpendicular to the slenderness axis and through a preferred bendingaxis chosen following the deformation pattern.

By way of non-limiting examples, the preferred bending axis will be avertical axis Z in a benchmark vehicle for a side rail and a horizontalaxis X for a center pillar.

The central longitudinal section of a piece is not necessarily flat. Itcould be curved.

In cases involving a straight-lined piece of constant cross-sections,the central longitudinal cross-section is however flat. This flatlongitudinal central plane section can pass through, for example, halfof the width or the thickness of a piece.

In cases where a “piece” in accordance with the invention is formed bythe assembly of several initially individual bodies, yet joined togetherthrough assembly, the central longitudinal cross-section is alongitudinal cross-section that passes through centers of inertia orgravity of two straight transverse cross-sections of the assembly ofsaid elements.

In FIG. 8a we have shown the cross-section of a beam 100 formed by theassembly of two hat-shaped pieces 102, 104 of the type illustrated inFIG. 1 a, coupled together and assembled at the level of their flanges30, 32. The beam 100 extends according to a longitudinal elongation orslenderness axis 106 that corresponds, for example, to an axis Y in abenchmark vehicle. Likewise, in FIG. 8a we have shown the chosenpreferred bending axis Z. Under these circumstances, and arbitrarily,the preferred bending axis Z extends within the plane of thecross-section and within a joint plane between the two pieces 102, 104.We have likewise represented in FIG. 8a bis a flat longitudinal centralplane section PM of a piece that passes through the slenderness axis 106and through the bending axis Z. The flat central longitudinal section PMpasses through centers of inertia or gravity of the two cross-sectionsections of the piece located close to the ends of the beam 100. Thecentral longitudinal section PM illustrated in FIG. 8a bis is merely anexample of the central longitudinal section of the beam illustrated,defined by the chosen preferred bending axis Z. The beam illustrated inFIG. 8a does indeed present unlimited central longitudinal sectionspassing through said centers of inertia or gravity, according the chosenpreferred bending axis.

In FIGS. 8b and 8b bis we have shown a piece 110 forming a center pillarcomprising a main portion 112 that extends according to a curvedelongation or slenderness axis 114 and that has a baseplate 116 and adissymmetric head 118. The elongation or slenderness axis 114 extendssubstantially according to a vertical axis Z in the benchmark vehicle.As has been shown in FIG. 8b , the piece 110 forming a center pillar isagain formed by the assembly of two hat-shaped pieces 102, 104 of thetype illustrated in FIG. 1a , coupled and assembled at the level oftheir flanges 30, 32 (in this case, the piece 104 is a covering piecewith walls 20, 22 lower in height than those of the walls 20, 22 of themain piece 102). Here the walls 20, 22 and the bottoms 10 of the piecethus extend vertically. Likewise, in FIG. 8b we have shown a chosenpreferred bending axis X (here horizontal in a benchmark vehicle). Inthis case, and arbitrarily, the preferred bending axis X extends withinthe plane of the cross-section and perpendicularly to the walls 20, 22of the main piece 102. Likewise, in FIG. 8b bis we have shown a flatcentral longitudinal section PM of a piece that passes through theslenderness axis 114 and through the bending axis X. The flat centrallongitudinal section PM passes through centers of inertia or gravity ofthe two straight transverse sections of the piece located close to theends of the beam or the central section of the piece 110 extending inaccordance with the main elongation axis 114. The central longitudinalsection PM illustrated in FIG. 8b bis follows the contour of the curvedelongation axis 114, and is curved in accordance with the curvaturethereof. The central longitudinal section PM illustrated in FIG. 8b bisis merely an example of the central longitudinal section of the beamillustrated, defined by the chosen preferred bending axis X. The beamillustrated in FIG. 8a does indeed present an unlimited number ofcentral longitudinal sections passing through said centers of inertia orgravity, according the chosen preferred bending axis.

In FIGS. 8c and 8c bis, we have shown a piece 120 forming side-railscomprising a straight-lined main portion 122 that extend according to anelongation axis or axis of extension 124. The elongation axis or axis ofextension 124 extends substantially according to a horizontal axis Y ina benchmark vehicle. As shown in FIG. 8c , the piece 120 formingside-rails is also formed by the assembly of two hat-shaped pieces 102,104 of the type shown in FIG. 1a , coupled and assembled at the level oftheir flanges 30, 32 (the piece 104 is a covering piece or inner coatingwith walls 20, 22 variante alternative). Here, the walls 20, 22 thusextend horizontally, whereas the bottoms 10 of the piece extendvertically. Likewise, in FIG. 8c we have shown a chosen preferredbending axis Z (herein vertical in a benchmark vehicle). In this case,and arbitrarily, the preferred bending axis Z extends in the plane ofthe cross-section and perpendicularly to the walls 20, 22 of the mainpiece 102. Likewise, in FIG. 8c bis we have shown a flat centrallongitudinal section PM of a piece that passes through the slendernessaxis 124 and through the bending axis Z. The flat central longitudinalsection PM passes through the centers of inertia or gravity of the twostraight transverse cross-sections of the piece located close to theends of the main section of the piece 120 extending according to themain elongation axis 124. The central longitudinal cross-section PMillustrated in FIG. 8c bis is flat. The central longitudinalcross-section PM illustrated in FIG. 8c bis is merely an example of thecentral longitudinal cross-section of the beam illustrated, defined bythe chosen preferred bending axis Z. The beam illustrated in FIG. 8cdoes indeed have unlimited central longitudinal cross-sections passingthrough said centers of inertia or gravity, according to the chosenpreferred bending axis.

In the FIGS. 8d and 8d bis, we represented a variant of piece 130forming a side-rail comprising a main curved longitudinal portion 132that extends according to a curved elongation or slenderness axis 134.The elongation or slenderness axis 134 extends substantially accordingto a horizontal axis Y in a benchmark vehicle. As has been representedin FIG. 8d the piece 130 forming a side-rail is again formed by theassembly of two hat-shaped pieces 102, 104 of the type illustrated inFIG. 1a , coupled and assembled at the level of their flanges 30, 32 (inthis case, the piece 104 is a covering or coating piece with walls 20,22 lower in height than those of the walls 20, 22 of the main piece102). The cross-section represented in FIG. 8d is geometricallyidentical to that of FIG. 8c , though swivelled 90° with respect to FIG.8c . Here, the walls 20, 22 thus extend vertically, whereas the bottoms10 of the piece extend horizontally. Likewise, in FIG. 8d we have showna chosen preferred bending axis Z (herein vertical in a benchmarkervehicle). In this case, and arbitrarily, the preferred bending axis Zextends in the plane of the cross-section and perpendicularly to thebottom 10 of the piece of the main piece 102. Likewise, in FIG. 8d biswe have shown a flat central longitudinal section PM of a piece thatpasses through the slenderness axis 134 and through the bending axis Z.The flat central longitudinal section PM passes through the centers ofinertia or gravity of the two cross-sections of the piece located closeto the ends of main portion of the piece 130, extending according to themain elongation axis 134. The central longitudinal section PMillustrated in FIG. 8d bis follows the contour of the curved elongationaxis 134, and is curved in accordance with the curvature thereof. Thecentral longitudinal section PM illustrated in FIG. 8d bis is merely anexample of the central longitudinal section of the beam illustrateddefined by the chosen bending axis Z. The beam illustrated in FIG. 8ddoes indeed have unlimited central longitudinal sections passing throughthe aforementioned centers of inertia or gravity, according to thechosen preferred bending axis.

The sectional drawing of the cross-sections shown in FIGS. 8a, 8b, 8cand 8d (sectional drawings perpendicular to the main longitudinal axisof the pieces) are referenced VIII-VIII in FIGS. 8a bis, 8 bbis, 8 cbisand 8 dbis.

As previously mentioned, the chosen bending axes depend on the desireddeformation. These are not limited to the models described above.Specifically, the bending axes are not necessarily perpendicular orparallel to the walls 20, 22 of the pieces, but may extend according toany angle with respect to said walls 20, 22, for example to 45° oranother angle in relation to these walls.

Following the description, by way of simplification, we shall use theexpression “longitudinal central plane”, which is by no means limiting.The expression “longitudinal central plane” will indeed be considered toencompass all of instances of “central longitudinal section”, even whenthis is not flat, thus conforming to the preceding definition.

In the context of this present application, “two areas respectivelyarranged on one side and the other”, is to be understood as meaning twoareas that extend respectively on one side and the other of longitudinalcentral plane of the piece, without one or the other of the two areascovering said longitudinal central plane.

More precisely, we can see in FIG. 2a an embodiment of a piece of thetype illustrated in FIG. 1a that comprises three areas 60, 62, 64respectively and alternatively arranged on one side and the other oflongitudinal central plane PM of said piece, passing through thereference axis A-A, yet similarly and alternatively located in locationsseparated longitudinally along the length of the piece.

In the context of this present application, it is understood that “areasalternatively located in locations separated longitudinally along thelength of the piece” refers to areas that are located in the differentlocations in the piece, distributed longitudinally along the length ofthe piece, without said areas being adjoining.

According to the embodiment shown in FIG. 2a , areas 60, 62 and 64 areessentially defined on the walls 20, 22 of the piece. When appropriate,the areas 60, 62 and 64 may be similarly extended at least in part onthe transition areas between the walls 20, 22 and the bottom 10 of thepiece and/or the flanges 30, 32, likewise in part on the bottom 10 ofthe piece and/or the flanges 30, 32.

A person skilled in the art will understand that such a piece enablesthe definition of points of weakness at the level of areas 60, 62 and64. These areas of weakness 60, 62 and 64 create, when subjected to anaxial load or lateral or transversal load on the PM plan is applied tothe piece, of preferred articulation areas determining a direction ofdeformation. This leads to a concertina folding of the piece, asillustrated in FIG. 2b , forming two portions slanted with respect tothe central plane PM of the piece in alternating directions. In FIG. 2b, we have shown the deformation of an angle a for certain portions ofthe piece, with respect to their original longitudinal plane. In thisway, the piece as a whole maintains a general direction centerd on thecentral plane PM.

In a more general sense, a person skilled in the art will understandthat arrangements in accordance with the present invention enables acontrolled deformation under compression and/or bending to be obtained,in other words, a deformation under only compression or deformationunder only bending or a deformation under a combination of compressionand bending, following the performance levels researched.

We can see in FIG. 2c an embodiment of a piece of the type illustratedin FIG. 1 a that constitutes a variant of FIG. 2a and contains areas 60,62, 64 respectively arranged on one side and the other of a longitudinalcentral plane PM of said piece which passes through the reference axisA-A, similarly and alternatively located alternatively in locationsseparated longitudinally along the length of the piece and having avarying length transversally to a plane of the cross-section of thepiece.

In the context of this present application, it is understood that“section” or “cross-section”, refer to a section of the piece passingthrough a plane perpendicular to the longitudinal or main axis of thepiece.

The varying width of areas 60, 62, 64, enables the concertinadeformation of the piece according to the reference axis A-A, as shownin FIG. 2b , to be improved despite the assymetry of the structure ofthe piece.

In FIG. 2d , we have shown a variant applied to a tubular piece of thetype illustrated in FIG. 1d for those alternating lower strength areas70, 72, 74, respectively located on one side and the other of alongitudinal central plane and in locations separated longitudinally,are limited to two opposite walls 40, 42, and in FIG. 2i the resultingdeformation.

It may be seen that these lower strength area 70, 72 and 74 are againformed in locations separated longitudinally along the length of thepiece. This arrangement enables, as shown in FIG. 2i , concertinafolding of the piece through the articulation around hinged areascreated by the lower strength areas 70, 72 and 74.

A variant is illustrated in FIG. 2e . According to this variant, theareas of lower strength 70, 71, 72, 73, 74 are alternatively carried outon each of the walls 40, 42 and 44, 46. And therefore, the lowerstrength areas 70, 71, 72, 73, 74 are formed in locations successivelyseparated longitudinally along the length of the piece. The areas oflower strength 70, 72, 74 formed in the opposite walls 40, 42, arestaggered by half with respect to the lower strength areas 71, 73 formedin the walls 44 and 46 to which they are perpendicular. The areas 70, 72and 74 are respectively located on one side and the other of alongitudinal central plane that passes through the axis A-A. Inaddition, the areas 71 and 73 are respectively located on one side andthe other of a longitudinal central plane that passes through the axisB-B.

In FIG. 2f , we have shown a variant applied to a tubular piece of thetype illustrated in figure 1d for which alternate lower strength areas70, 72, 74, respectively arranged on both sides of a longitudinalcentral plane, are limited to two opposing partitions 40, 42, and inFIG. 2g the resulting deformation. The areas 70, 72 and 74 arerespectively located on both sides of a longitudinal central plane thatpasses through the axis A-A.

We note here that the piece comprises additional lower strength areassuch that two lower strength areas 70 a, 70 b, respectively 72 a, 72 bare formed in relation to the identical locations, longitudinally alongthe length of the piece. As shown in FIG. 2g , this arrangement enablesthe piece to fold as a result of collapsing on itself such that thepiece remains, at all points along its length, substantially centerd onthe longitudinal central plane PM passing through the reference axisA-A.

Another variant is illustrated in FIG. 2h . According to this variant,the areas of lower resistance, 70, 71, 72, 73, 74 are alternativelycarried out on opposite pairs of four walls 40, 42 and 44, 46. Andtherefore, the lower strength areas 70 a, 70 b; 71 a, 71 b; 72 a, 72 b;73 a, 73 b; 74 a, 74 b are formed in regard to identical locationslongitudinally along the length of the piece, but areas of lowerstrength 70 a, 70 b; 72 a, 72 b; 74 a, 74 b formed on the walls 40, 42,are staggered by half with respect to the lower strength areas 71 a, 71b; 73 a, 73 b formed in the walls 44 and 46. The areas 70, 72 and 74 arerespectively located on one side and the other of a longitudinal centralplane that passes through the axis A-A. Areas 71 and 73 are respectivelylocated on one side and the other of a longitudinal central plane thatpasses through the axis B-B.

FIGS. 2i, 2j and 2k display three non-limiting examples of controlleddeformations likely to be obtained as a result of the invention, with atleast two hinged lower strength areas of the type illustrated in FIGS.2a, 2c or 2 d. More precisely the FIGS. 2i, 2j and 2k display threenon-limiting examples of controlled deformations likely to be obtainedas a result of the invention, respectively for

FIG. 2i with 3 or 4 hinged lower strength areas of the type illustratedin FIG. 2a, 2c or 2 d,

FIG. 2j with 2 hinged lower strength areas of the type illustrated inFIG. 2a, 2c or 2 d and

FIG. 2k with axial juxtaposition of 2 hinged lower strength areas of thetype illustrated in FIGS. 2a, 2c or 2 d and one assembly designed tocollapse on itself, which incorporates hinged lower strength areas ofthe type illustrated in FIGS. 2f or 2 h.

A person skilled in the art will understand that the embodiment shown inFIG. 2a corresponds to an embodiment according to which the metal piecein accordance with the present invention comprises at least one lowerstrength area of mechanical strength, defined during stamping and thatextends to at least one of the walls, dissymmetrical with respect to thereference axes A-A and B-B, in this case at least with respect to thereference axis A-A.

The fact that two asymmetric lower mechanical strength areas have beenprovided with respect to the reference axes and, when appropriate, witha varying width as shown below, enables the orientation of thedeformations created under stress to be finely controlled.

In the case where a piece has an asymmetric section with respect to thecentral plane PM, as shown for example in FIG. 3e , the use of a varyingwidth for at least certain lower mechanical strength areas 50 enable,for example, a bending axis maintained in this central plane to beimposed, due to the structural dissymmetry of the piece, a weakermechanical strength area would lead to an inclined bending axis withrespect to the central plane.

Generally, in this lower mechanical strength area there will be anincreasing width towards the sectors of the piece with a more complexstraight structure and thus in theory have a greater mechanicalstrength.

The aforementioned arrangement of the varying width similarly allowsfor, should this be desired, a symmetrical piece with respect to thecentral plane or any reference axis, to impose a bending axis that isnot orthogonal to this reference or inclined axis with respect to thecentral plane of reference, and thus impose the deformation direction ofthe piece.

In the FIGS. 3a to 3f , we have shown six exemplary embodiments of apiece of the type illustrated in FIG. 1 a having areas 50 of lowermechanical strength than the rest of the body, formed during stamping ofthe piece and which has a varying width transversally with respect tothe cross-section plane of the piece. This arrangement, namely the useof the lower mechanical strength having a varying width, which enablesthe deformation direction of the piece to be controlled whilst bending.

The areas of lower mechanical strength are shown in cross-hatching inFIGS. 3a to 3 f.

A person skilled in the art will understand that these pieces containareas of lower mechanical strength, which are dissymmetric with respectto the reference axes.

More accurately, according to FIG. 3a , the areas 50 are formed on allof the section of the piece and thus extend towards the bottom 10 of thepiece, the walls 20, 22 and the grooves 30 and 32.

According to FIG. 3b , the areas 50 are formed on the bottom 10 of thepiece.

According to FIG. 3c , the areas 50 are essentially formed on the walls20, 22 and partly in the transitions between the walls 20, 30 and thebottom 10 of the piece.

According to FIG. 3d , the areas 50 are essentially formed on a flange30.

Moreover, FIG. 3e shows another embodiment of a variant of pieceinspired by the hat type illustrated in FIG. 1 a, but in which the basebody, or bottom 10 is not symmetrical with respect to the reference axisA-A. In this case, one of the walls 20 is larger than the other wall 22.The piece includes at least part of this wall 20, an area 50 of lowermechanical strength with which the rest of the body is formed during thestamping of the piece and this area 50 extends to the bottom 10 of thepiece.

In addition, this piece comprises an area of lower mechanical strength,which is dissymmetric with respect to the reference axes.

According to the embodiments represented in the FIGS. 3a to 3e , thesides of the areas 50 of lower mechanical strength are substantiallyrectilinear and inclined inwards.

In FIG. 3f , we have shown another embodiment according to which theareas 50 of lower mechanical strength have non-rectilinear sides thatare curved and have a general ovoid shape, for example on wall 20.

A person skilled in the art could come up with numerous other embodimentvariants, notably in the areas of lower mechanical strength in theneighbouring transition areas of the crosshatched areas represented inthe attached figures.

The areas of lower strength have variable widths according to themethods of production shown in the FIGS. 2c, 2d, 2e, 2f and 2 h.

One can tell that according to the FIGS. 2c and 2d the width variationsin areas of lower mechanical strength are identical along the entirelength of the piece. However, according to embodiments shown in theFIGS. 2f and 2h , the width variations in said areas alternate, meaningthey alternately increase and decrease in opposite directions to thesection of the piece.

Preferably, the areas of lower mechanical strength are carried out bylocal control of the stamping temperature during a stamping process ofthe piece.

More precisely, the invention preferably implements a process comprisingsteps consisting of:

heating the piece to a temperature range suitable for obtaining anaustenitic stage,

then stamping this piece in a stamping tool, comprising a least twocomplementary elements, respectively constituting the functions of punchand mould, among which the piece to be formed is stamped, adapted inorder to define the different temperatures on different areas of thestamped piece with the aim of imposing different cooling methods ondifferent areas on the piece.

Each of these punches and molds may be formed by the assembly of severaljuxtaposed blocks according to the geometry and dimensions of the piecein question.

The areas of the piece in contact with parts of the cooled stampingtool, are stamped at controlled temperatures leading to areas of highermechanical strength, typically in excess of 1400 MPa, whereas the areasof the piece stamped at higher temperatures leads to areas of lowermechanical strength typically below 1100 MPa, for example comprisedbetween 500 and 1000 MPa.

Lower mechanical strength in certain areas of the stamped piece may beobtained thanks to high local stamping temperatures, for examplehollowing out areas in the stamping tool in such a way that thepre-heated piece can be cooled and/or have its stamping temperaturelocally increased, for example to help heating strength introducedlocally in these stamping blocks.

Likewise, areas of the stamping blocks may be cooled, for example withthe help of channels formed in these stamping blocks and in whichcooling fluid circulates.

The present invention involves pieces made from steel.

It can be applied to all types of pieces implemented in an automobilevehicle, by means of non-limiting example, a center pillar or side-rail,or even in a shock absorber to absorb energy.

During compressed axial load, the areas of lower strength form hingeddeformation areas that enable the direction of lateral deformation ofthe elongated piece to be oriented and thus avoids random deformation ofthe pieces.

The invention enables, for example, the deformation of side-rails to beoriented towards the outside of the passenger compartment and towardsthe inside thereof, thus minimising the risk of impact for the occupantsof the passenger compartment.

The invention notably enables the absorption of energy to be optimised,should an accident occur.

It similarly enables the acceleration peaks felt by the occupants of avehicle to be reduced, should an accident occur.

It is clearly understood that the present invention is not limited toembodiments that have been outlined herein, but rather extends to allvariants corresponding to the same essence.

For example, the general U-shaped piece illustrated in FIG. 1a can becompleted by a covering plate as illustrated in the FIGS. 8a, 8b, 8c and8 d.

Furthermore, the inclusion of assembled braced and/or stiffening ribslocated on certain sides of the piece.

The term “metal piece”, in the context of this invention, must beunderstood in its broadest sense to cover all unassembled single-blockstructures and to structures formed by the assembly of several initiallyindividual bodies, later joined together during assembly.

We have illustrated in the FIGS. 6A, 6B and 7A, 7B pieces ofgeometrically identical cross-sections formed by two elementary h-shapedpieces C1 and C2 of the type illustrated in FIG. 1a , mounted head totail and fixed in place by their flanges. The two pieces illustrated inthe FIGS. 6A, 6B and 7A, 7B, respectively conforming to this invention,are distinguished by the fact that the piece illustrated in FIGS. 6A, 6Bconforming to the present invention comprises an area of lowermechanical strength 50 limited to one of the bottoms 10 of the pieces ofC2 and a part adjacent to the walls 20, 22, whereas the pieceillustrated in the classic FIGS. 7A, 7B comprises an area of lowermechanical strength in the entirety of its cross-section.

We have illustrated in the FIGS. 6Abis and 6Bis a variant of the pieceaccording to the present invention with the same geometry as FIGS. 6Aand 6B (two elementary hat-shaped pieces C1 and C2 of the typeillustrated in FIG. 1a , mounted head to tail and fixed in place bytheir flanges), yet comprising an area of lower mechanical strength 50that covers all of one of the C2 two elementary pieces, or half of thecomplete piece formed by the assembly of two elementary pieces C1 andC2.

FIG. 5 represents the curve A of the bending moment around preferredaxis Z of the piece according to the present invention according to FIG.6A during bending around an axis parallel to the axis B-B (axe Z) asshown in FIG. 6C, the curve B of the bending moment around the same axisZ of the classic piece during bending around an axis parallel to theaxis B-B as shown in FIG. 7C and the curve C of the bending momentaround the same axis Z of the piece according to the present inventionaccording to FIG. 6Abis during bending around an axis parallel to theaxis B-B as shown in FIG. 6Cbis.

The examination comparing curves A and B shows that the inventionenables higher bending moment (around +18% in this case) to be obtained.

FIG. 4 represents a comparative diagram of the bending moments obtainedaccording to 4 bending axes, respectively for the piece in accordancewith the invention represented in FIG. 6A containing an area of lowermechanical strength limited to part of the cross-section thereof and forthe classic piece represented in FIG. 7A having an area of lowermechanical strength on the entirety of its cross-section.

More precisely, in FIG. 4 we have shown a diagram of the bending momentsfor 4 bending axes, Mz+ and Mz− corresponding to two flexion directionsin opposite directions around an axis parallel to the axis B-B, whereasMy+ and My− correspond to two flexion directions in opposite directionsaround an axis parallel to the axis A-A.

The examination of the FIG. 4 shows that the present invention allowsfor an identical section of the piece that can improve performancelevels due to the increase in the range of the bending moment in the 4bending axes and mainly in the 3 bending axes not devised for improvingthe overall robustness of the piece according to the desired/preferredbending axis (in other words, ensuring constant operationalfunctionality during bending according to the desired/preferred bendingaxis to control the differences between moments according to thedifferent axes), and this without causing risk of rupture.

FIG. 4 shows increase according to the invention of around +25°according to the bending axis Y, +37° as per the bending axis −Z, +25°as per the bending axis −Y and +18° as per to Z bending axis.

In FIGS. 9 and 10, we have shown curves that are based on the plots ofthe diagram represented in FIG. 4.

FIG. 9 represents the curve A of the bending moment around axis Y of thepiece in accordance with the present invention according to FIG. 6Aduring bending around an axis parallel to the axis A-A (axis Y) as shownin FIG. 6D, the curve B of the bending moment around the same axis Y ofthe classic piece during bending around the same axis parallel to theaxis B-B, as shown in FIG. 7D and the curve C of the bending momentaround the same axis Y of the piece in accordance with the presentinvention according to FIG. 6Abis during bending around an axis parallelto the axis B-B.

The examination compared the A and B curves represented in FIG. 9showing that the invention enables a higher moment (in the region of+25% in this case) to be obtained.

FIG. 10 contains the A, B and C curves illustrated in FIG. 5 for bendingaround axis Z as shown in FIG. 6C1 and represented moreover in curve A1obtained due to bending according to the axis Z, of a piece inaccordance to the invention according to FIG. 6A, but in the oppositedirection to the one shown in FIG. 6E.

The comparison examination of the A, B and A1 curves represented in FIG.10 show that the invention a higher moment (to the order of +18% in thiscase for bending according to Z as indicated above and +37% for bendingaccording to −Z) to be obtained.

1. A metal piece, particularly for the production of an automobilevehicle, comprising: at least two areas of lower mechanical strengththan a body of the piece, respectively arranged on one side and anotherside of a longitudinal central section (PM) of the piece andalternatively located in locations separated longitudinally along thelength of the piece, and without the areas being adjoined.
 2. The pieceaccording to claim 1, wherein the areas of lower mechanical strengththan the body of the piece are formed by local control of a stampingtemperature during a stamping process of the piece.
 3. A stampingprocess for making the piece according to claim 1, wherein the areas oflower mechanical strength than the body of the piece are formed by alocal control of a stamping temperature during a stamping process of thepiece, the stamping process comprising the steps of: heating apre-formed piece to a temperature range suitable for obtaining anaustenitic stage, then stamping the pre-formed piece in a stamping toolsuitable for defining different temperatures in different areas of astamped piece, including one of local recesses formed in the stampingtool or by local heating of the stamping tool.
 4. The piece according toclaim 1, wherein the body of the piece has a mechanical strength above1400 MPa, whereas the areas of lower mechanical strength have amechanical strength lower than 1100 MPa.
 5. The piece according to claim1, wherein the piece further comprises at least one additional area oflower mechanical strength than the body of the piece, such that thepiece has areas of lower mechanical strength than the body of the piecerespectively arranged on the one side and the other side of thelongitudinal central plane (PM) and formed in longitudinally identicallocations along a length of the piece.
 6. The piece according to claim1, wherein the piece comprises a bottom of the piece and two flangesseparated from the bottom by walls and the piece comprises an area oflower mechanical strength defined during a stamping process and having avarying width perpendicular to a cross-section of the piece.
 7. Thepiece according to claim 1, wherein the areas of lower mechanicalstrength than the body of the piece are delimited by areas withrectilinear edges.
 8. The piece according to claim 1, wherein the areasof lower mechanical strength than the body of the piece are delimited byareas with curved edges.
 9. The piece according to claim 1, wherein thepiece comprises at least two areas of lower mechanical strength than thebody of the piece distributed thereon and having variations in identicalwidth along an entire length of the piece.
 10. The piece according toclaim 1, wherein the piece comprises at least two areas of lowermechanical strength than the body of the piece distributed thereon andhaving variations in width alternatively in opposite directions, alongan entire length of the piece.
 11. The piece according to claim 1,wherein the areas of lower mechanical strength are defined on the wallsof the piece.
 12. The piece according to claim 1, wherein the piececomprises a bottom and two side flanges separated from the bottom bywalls, a section of the piece being defined by two reference axes (A-A),one substantially orthogonal to the bottom of the piece and the othersubstantially parallel to at least one flange, and the piece comprisingan area of lower mechanical strength defined during a stamping of thepiece and which extends over at least one of the walls, asymmetricallywith respect to the two reference axes.
 13. The piece according to claim1, wherein the areas of lower mechanical strength extend at leastpartially into transition areas between walls and a bottom of the piece,and/or flanges or part of the bottom of the piece and/or the flanges.14. The piece according to claim 1, wherein the piece comprises at leastone portion on which the at least two areas of lower mechanical strengththan the body of the piece, are respectively arranged on one side andthe other side of the longitudinal central section (PM) of the piece andalternatively located in locations separated longitudinally along thelength of the piece and, at least one portion on which at least twoareas of lower mechanical strength than the body of the piece, arerespectively arranged on one side and the other of a longitudinalcentral section (PM) of the piece and located facing in the same placesalong the length of the piece.
 15. The piece according to claim 1,wherein the piece is a side-rail.
 16. A metal piece, particularly forthe production of an automobile vehicle, comprising: at least two areasof lower mechanical strength than a body of the piece, respectivelyarranged on one side and another side of a longitudinal central section(PM) of the piece and alternatively located in locations separatedlongitudinally along the length of the piece, and without the areasbeing adjoined; wherein the body of the piece has a mechanical strengthof above 1400 MPa and the areas of lower mechanical strength have amechanical strength of below 1100 MPa.
 17. The piece according to claim16, wherein the areas of lower mechanical strength are formed by localcontrol of a stamping temperature during a stamping process of thepiece.
 18. A method for making the piece according to claim 16, whereinthe areas of lower mechanical strength than the body of the piece areformed by local control of a stamping temperature during a stampingprocess of the piece, comprising the steps of: heating the piece to atemperature range suitable for obtaining an austenitic stage, thenstamping this piece in a stamping tool suitable for defining differenttemperatures in different areas of the stamped piece, including localrecesses formed in the stamping tool or by local heating of the stampingtool.
 19. The piece according to claim 16, further comprising at leastone additional area of lower mechanical strength than the body of thepiece, such that the piece has areas of lower mechanical strength thanthe body of the piece respectively arranged on the one side and theother side of the longitudinal central plane (PM) formed inlongitudinally identical locations along the length of the piece.
 20. Ametal piece, particularly for the production of an automobile vehicle,comprising: at least two areas of lower mechanical strength than a bodyof the piece, respectively arranged on one side and another side of alongitudinal central section (PM) of the piece and alternatively locatedin locations separated longitudinally along the length of the piece, andwithout the areas being adjoined; wherein the areas of lower mechanicalstrength than the body of the piece are formed by a local control of astamping temperature during a stamping process of the piece.